Sparingly soluble calcium salts wer

Sparingly soluble calcium salts were studied as reactants in the synthesis of needle-like precipitated calcium carbonate (PCC). The morphology and aspect ratio of the PCC particles were characterized with SEM. Polymorphs and crystal size were characterized using X-ray diffraction. The counterions of the sparingly soluble salts influenced the growth kinetics of PCC as well as the polymorphism and morphology of product particles. Either chrysanthemum-like or needle-like aragonite can be synthesized from calcium sulfate and sodium carbonate depending on the supersaturation and synthesis conditions. Low concentration and slow addition rate of sodium carbonate solution were favorable to the formation of aragonite. Addition of sodium sulfate to the reaction system (calcium chloride and sodium carbonate) promoted the formation of aragonite and decreased the crystal size of aragonite due to the decrease of supersaturation and adsorption of sulfate ion. Too much added sodium sulfate, however, did not further increase the aragonite fraction. An optimal temperature for the formation of aragonite was found to be ca. 60 °C. Slow dissolution kinetics of sparingly dissoluble salt also is very important for controlling PCC polymorphism and morphology.